The invention relates to a double-edged milling cutter which is formed by a milling cutter body and a single cutting tip (insert).
Such a milling cutter is part of the group of milling cutters which are mostly provided with a receiving shank, with the cutting tip being received in a transverse recess of the milling cutter body such that it projects with its sides from two diametrically opposed sides of the body as well as in axial direction. The two projecting sides constitute the cutting edges. The cutting tip can have various forms, in particular it may have cutting edges that are almost parallel to the axis of the milling cutter, or in case of more widespread cutters it may have a partly spherical shape.
The present specification, for reasons of simplification, relates only to milling cutters of the partly circular type, with the milling cutter with such a cutting tip being referred to also as "spherical" in practical application, with this including however also cutting tips of other shapes. In general, such milling cutters are capable of milling also with axial feed and thus are referred to as "drilling milling cutters"; they find application also when milling free shapes (copy milling).
FIG. 6 of the drawings schematically shows a type of milling cutter according to the prior art. FIG. 6 shows a milling cutter body 10 and a double-edged cutting tip 11. Formed in the milling cutter body is a recess 12 having two mutually opposed sidewalls 13 and 14 for receiving the cutting tip 11 provided with a bore 15 for receiving a mounting screw 16.
One wall 13 of recess 12 has a through-bore 13' for the head of the mounting screw 16, whereas the other wall 14 is provided with a threaded bore 14' in which mounted screw 16 is threadedly received. The cutting tip 11 in turn has an axial back 11' abutting a bottom wall 12' of the recess 12 for the cutting tip.
The back 11' of the cutting tip and the floor 12' of the recess in some cases are provided with designs of different nature, having the purpose of centering the cutting tip with respect to the axis of the milling cutter. However, in most cases such centering is obtained by a perfect cylindrical alignment between the mounting screw 13 and the bore 15 of the cutting tip, as can be seen from FIG. 6.
For the preparation of the milling cutter, the cutting tip is introduced into the recess; the screw is inserted into the bore within the first wall, then through the bore in the cutting tip itself and then it is threadedly engaged with the threaded bore of the other wall. By tightening of the screw up to a stop, the two parallel walls of the recess are urged together in the manner of pliers and they thus lock the cutting tip. The system according to the prior art as described hereinbefore has found extensive distribution, however the use thereof has revealed some insufficiencies.
One insufficiency resides in the fact that, upon clamping of the cutting tip, part of the force developed by the screw 16 by the torque (moment) applied to the screw is consumed for bending the walls 13 and 14 of recess 12. The consequence is that the force effectively available for retaining the cutting tip frequently is insufficient for ensuring mounting in the manner required for the cutting tip so that the latter does not become instable during use.
Another insufficiency results from the fact that walls 13 and 14 of the recess, which theoretically should be symmetrical, hardly are so in reality, which is due to manufacturing tolerances, non-homogeneity of the material, different configurations (one wall contains the through-bore and the recess for the screw head, the other wall contains the threaded bore), so that the walls have different bending strengths, due to which the amount of bending of the two walls is not uniform, whereby the possibility is lost of performing milling with axial feed.
An additional insufficiency results from the fact that the resistance moment acting on the milling cutter, and thus on the cutting tip, during use thereof may be a cause to the effect that the walls of the recess receiving the cutting tip are spread apart, so that the cutting tip becomes instable, with the result that the milling cutter cannot be used any more in case of such spreading.
The present invention seeks to solve the above explained problems and to provide a milling cutter with increased strength and reliability, i.a. a milling cutter which displays higher precision and increased performance during use.